Compression ultrasound for deep vein thrombosis

What it is

Compression ultrasound diagnoses deep vein thrombosis (DVT) by one simple sign: a normal vein collapses completely under gentle probe pressure, while a vein containing thrombus does not. Fresh clot can be as black as flowing blood, so compression, not appearance, is the key. The bedside version (two-region or two-point compression) checks the common femoral vein in the groin, down through the saphenofemoral junction and the femoral bifurcation, and the popliteal vein behind the knee. A whole-leg scan, usually done by radiology or a vascular laboratory, also checks the femoral vein along the thigh and the calf veins, often with Doppler. The test is read together with pretest probability (a clinical score such as Wells) and D-dimer.

What to check

• Fully compressible vein = no clot at that spot; non-compressible vein = DVT.
• Acute clot: the vein is often distended and the clot dark, sometimes nearly black; chronic clot is brighter, the wall thick and the vein partly compressible.
• The femoral vein (formerly called the «superficial» femoral vein) is a deep vein; clot there is a DVT.
• The artery stays round under the same pressure; that is the internal control that enough pressure was used.
• A two-region scan does not see the calf veins; a whole-leg scan does.

Reading it step by step (and why)

1. Patient supine, head up slightly, leg turned out with the knee bent — veins fill and the groin and back of knee open up.
2. Linear high-frequency probe, transverse to the vessel — the veins are shallow and the cross-section shows full collapse.
3. Find the common femoral vein beside the artery at the groin — it lies medial to the artery; the artery is the pressure control.
4. Press firmly enough to dent the artery — the vein walls must touch completely; any gap left means clot.
5. Move down in steps: saphenofemoral junction, then where the femoral and deep femoral veins split — clots often start at junctions.
6. Scan the popliteal vein behind the knee down to the calf branches — it lies nearer the skin than the artery from this approach.
7. Keep the view transverse while compressing — in long axis the probe can slide off the vein and fake a normal result.
8. Add colour Doppler only as support — the decision rests on compression, not on colour.

Common mistakes

• Not pressing hard enough, especially in obese legs or a deep popliteal fossa, gives a false-positive result.
• Mistaking a lymph node in the groin or a Baker's cyst behind the knee for a thrombosed vein; follow the structure up and down.
• Compressing in long axis and sliding off the vein.
• Calling a negative two-region scan «no DVT» in a high-probability patient: calf clots can extend later.
• Reading an old (chronic) clot as a new one in a patient with previous DVT; compare with prior scans.

Next step

• Low pretest probability: D-dimer first; if negative, no ultrasound is needed.
• Non-compressible deep vein: treat as DVT and start anticoagulation unless contraindicated; consider pulmonary embolism if breathless.
• Negative two-region scan with high probability or positive D-dimer: repeat in about one week or request a whole-leg ultrasound.
• Unclear findings, possible chronic clot, or iliac or calf vein questions: request a formal venous duplex from radiology or the vascular laboratory.
• Massive leg swelling with a cold, blue limb: call vascular surgery at once.

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Elsewhere in DurgiPedia

• Signs of deep vein thrombosis: Homans and the Wells score
• Varicose veins: the Trendelenburg (Brodie–Trendelenburg) test

Connections

← All of radiology

Educational content; it does not replace a radiologist's report and is not a clinical instruction. Each study is ordered on the patient's assessment and your institution's protocols.

Sources: Point-of-Care Ultrasonography for Deep Venous Thrombosis (StatPearls (NCBI Bookshelf), 2023); Deep Venous Thrombosis (StatPearls (NCBI Bookshelf), 2023).

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